Low coefficient of thermal expansion (CTE) thermosetting resins for integrated circuit applications

ABSTRACT

An embodiment of the present invention is a technique to form a resin. A mixture is formed by a curing agent dissolved in the epoxy resin. The epoxy resin contains a first rigid rod mesogen. The curing agent contains a second rigid rod mesogen and one of a hydroxyl, amine, and anhydride.

BACKGROUND

1. Field of the Invention

Embodiments of the invention relate to the field of semiconductor, andmore specifically, to semiconductor materials.

2. Description of Related Art

The next generation die interlayer dielectric (ILD) materials are porousand poor mechanical strength. Low CTE materials may be used to reducethe stresses on the ILD due to coefficient of thermal expansion (CTE)mismatches between materials in the package. In addition, sincematerials flow over greater distances through narrower gaps, theconcentration of the filler, which is typically used to reduce the CTE,may be eliminated, reduced, or minimized.

Existing techniques to reduce the CTE and at the same time reduce oreliminate the concentration of the filler has a number of disadvantages.One technique uses an epoxy resin filled with 40-80 weight percent ofsilica filler. This technique may reduce the CTE but also gives highmodulus and high viscosity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1A is a diagram illustrating a semiconductor package in which oneembodiment of the invention can be practiced.

FIG. 1B is a diagram illustrating a semiconductor device in which oneembodiment of the invention can be practiced.

FIG. 2 is a diagram illustrating a structure of an epoxy resin accordingto one embodiment of the invention.

FIG. 3 is a diagram illustrating a structure of a curing agent accordingto one embodiment of the invention.

FIG. 4 is a diagram illustrating a process to form the resin accordingto one embodiment of the invention.

DESCRIPTION

An embodiment of the present invention is a technique to form a resin. Amixture is formed by a curing agent dissolved in the epoxy resin. Theepoxy resin contains a first rigid rod mesogen. The curing agentcontains a second rigid rod mesogen and one of a hydroxyl, amine, andanhydride.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown to avoidobscuring the understanding of this description.

One embodiment of the invention may be described as a process which isusually depicted as a flowchart, a flow diagram, a structure diagram, ora block diagram. Although a flowchart may describe the operations as asequential process, many of the operations can be performed in parallelor concurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed.A process may correspond to a method, a procedure, a method ofmanufacturing or fabrication, etc.

One embodiment of the invention is to provide a thermosetting resinincluding in the polymer backbone greater than 50 weight percentage of arigid rod mesogen and having, after cure, an isotropic CTE less than 40ppm/° C. The resin may be processable at temperatures below 150° C. andcurable at temperatures below 200° C. The resulting resin is useful forintegrated circuit (IC) applications including being used as underfill,mold compound, die attach, substrate dielectric, and similar elements.These applications may also be used in IC packaging.

FIG. 1A is a diagram illustrating a package 100 in which one embodimentof the invention can be practiced. The package 100 includes asemiconductor device 105, lead frames 110, die bond 115, platings 120,metal conductor 125, and a resin 130.

The semiconductor device 105 is any integrated circuit (IC) device. Itmay be fabricated by any Metal Oxide Semiconductor (MOS) technology. Itmay be a memory chip, a processor, a chipset, a logic device, amicro-controller, a microprocessor, etc. The lead frames 110 provideinterconnections to other devices or elements. They may be made ofcopper or copper alloy or any other suitable conducting material. Thedie bond 115 provides electrical connections between the semiconductordevice 105 and the lead frame 110.

The plating 120 provides contact interface between the semiconductordevice 105 and the metal conductor 125. It may be made of silver toprevent oxidation and maintain conductivity of the metal conductor 125.The metal conductor 125 provides electrical connection between thesemiconductor device 105 and the lead frame 110. It may be made ofcopper or copper alloy. The resin 130 provides sealing to the entireassembly. The resin 130 has a low CTE and is made by one embodiment ofthe invention.

FIG. 1B is a diagram illustrating a semiconductor device 140 in whichone embodiment of the invention can be practiced. The semiconductor 140includes a substrate 150, an interconnection layer 155, an electrode160, a protection layer 165, a bump 170, a lead 175, and a resin 180.

The substrate 150 is any substrate layer in a typical semiconductordevice. It may be a silicon layer. The interconnection layer 155provides a number of layers of insulators and conductors for theintegrated circuit. The electrode 160 is typically formed at theperiphery of the device. The protection layer 165 provides protectionfor the interconnection layer 155 and an interface to the resin 180. Itis typically made of resin of the polyimide group. The bump 170 provideselectrical and mechanical interface between the electrode 160 and thelead 175. The bump 170 may be made by gold and bonded to the electrode160. The lead 175 provides interconnection between the device 140 andother devices.

The resin 180 is deposited or coated on the protection layer 165. It istypically cured in a heat treatment process. The resin 180 has low CTEand is made by one embodiment of the invention.

FIG. 2 is a diagram illustrating a structure of an epoxy resin 200according to one embodiment of the invention.

The epoxy resin 200 contains a rigid rod mesogen 210. The rigid rod likemesogen 210 contains molecules which are components of liquidcrystalline materials. Studies indicate that the CTE of an unfilled,unoriented epoxy resin comprising a rigid rod mesogen which inducesliquid crystallinity decreases to 45 ppm/° C. with increasing mesogenconcentration. It is expected by increasing greater than 50% weightpercentage of a rigid rod mesogen, the CTE is decreased further to below40 ppm/° C. In one embodiment, the epoxy resin is epoxylated3,3′,5,5′-tetra-methylbiphenol.

FIG. 3 is a diagram illustrating a structure of a curing agent 300according to one embodiment of the invention.

The curing agent 300, or the crosslinker, is formed by a rigid rodmesogen 310 and element X 320. The element X 320 is selected from agroup consisting of hydroxyl (—OH), amine (—NH₂), and anhydride(—COOOC—).

In one embodiment, the curing agent 300 is 4,4′-diphenol where X=OH.Because of the high melting point of the 4,4′-diphenol (about 180° C.),the epoxy resin 200 and the curing agent 300 are pre-mixed in astoichometric ration of one mole of epoxy to one mole of phenol atapproximately 150° C., in order to dissolve the curing agent 200 in theepoxy resin 300. This mixture, which has a melting point below 150° C.,is then used to prepare for the final formulation. A variety ofadditives may be added to the mixture. These additives include catalyst,adhesive, flow aids, mold release agents, colorants, and otheradditives. Optionally, a filler may be added to the mixture to furtherreduce the CTE of the resulting material.

In another embodiment, the curing agent 300 is 4,4′-dianiline (X═NH₂).Due to the relatively low melting point of the 4,4′-dianiline (about128° C.), the material may be used directly to prepare the finalformulation or may be pre-mixed.

By using the epoxy resin and the curing agent both containing a rigidrod mesogen, the weight percentage of the mesogen is essentiallydoubled, allowing achievement of approximately 70-80 weight percentmesogen, or a percentage that is higher than 50%. This weight percentageof mesogen gives a CTE below 40 ppm/° C.

FIG. 4 is a diagram illustrating a process 400 to form the resinaccording to one embodiment of the invention.

Upon START, the process 400 forms an epoxy resin containing a firstrigid rod mesogen (Block 410). In one embodiment, the epoxy resin isepoxylated 3,3′,5,5′-tetra-methylbiphenol. Next, the process 400 forms acuring agent containing a second rigid rod mesogen and one of ahydroxyl, amine, and anhydride (Block 420). In one embodiment, thecuring agent is one of 4,4′-diphenol and 4,4′-dianiline. Then, theprocess 400 dissolves the curing agent in the epoxy resin to form amixture (Block 430). This can be performed by pre-mixing the epoxy resinand the curing agent in a stoichiometric ratio of one mole of epoxy toone mole of phenol at approximately 150° C.

Next, the process 400 adds at least an additive to the mixture (Block440). The additive may be any one of a catalyst, an adhesive, a moldrelease agent, and a colorant, or any other additives. Then, the process400 adds a filler to the mixture (Block 450) and is then terminated.Blocks 440 and 450 may be performed alternatively, separately,sequentially or in parallel.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

1. A method comprising: forming an epoxy resin containing a first rigidrod mesogen; forming a curing agent containing a second rigid rodmesogen a hydroxyl; and dissolving the curing agent in the epoxy resinto form a mixture such that the mixture has a weight percentage ofmesogen higher than 50%; wherein the dissolving comprises pre-mixing theepoxy resin and the curing agent in a stoichiometric ratio of one moleof epoxy to one mole of phenol at a first temperature.
 2. The mcthod ofclaim 1 further comprising: adding to the mixture at least an additive.3. The method of claim 2 wherein adding comprises: adding to the mixtureat least the additive being one of a catalyst, an adhesive, a moldrelease agent, and a colorant.
 4. The method of claim 2 wherein addingfurther comprises: adding a filler.
 5. The method of claim 1 whereinforming the epoxy resin comprises: forming the epoxy resin beingepoxylated 3, 3′, 5, 5′-tetra-methylbiphenol.
 6. The method of claim 1wherein forming the curing agent comprises: forming the curing agentbeing 4, 4′-diphenol.
 7. The method of claim 1 wherein the firsttemperature is approximately 150 degrees Celsius.
 8. The method of claim1 wherein the mixture has a coefficient of thermal expansion (CTE) lessthan 40 ppm/° C.